Method of making a tubular member

ABSTRACT

A flexible strip of material is formed into a spiral shape having two overlapping layers by passing a flat strip through a series of apertured elements having particular shaped tapered passageways and slots. The layers may be applied as insulation for conductors.

United States Patent METHOD OF MAKING A TUBULAR MEMBER [56] Relerences Cited UNITED STATES PATENTS 2,406,051 8/1946 Weiss 156/462 3,340,113 9/1967 Burr 156/54 3,360,409 12/1967 Jackimowicz et a1 156/54 FOREIGN PATENTS 872,741 2/1942 France 154/225 Primary Examiner- Benjamin A. Borchelt Assistant Examiner-H. J. Tudor I Attorneys-C. Cornell Rems'en, Jr., Walter Baum, Percy P.

Lantzy, Philip M. Bolton, lsidore Togut and Charles L. Johnson 6 Claims, 4 Drawing Figs.

U.S. Cl 156/54, AB$TRACT= A xi r p f m t rial isformed into a spiral 156/200, 156/462, 174/111 shape having two overlapping layers by passing a flat strip Int. Cl ..1101b 13/10 through a series of apertured l men having particular Field 01 Search 174/111; shaped tapered passageways and slots. The layers may be ap- 156/54, 462, 200 plied as insulation for conductors.

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Attorney METHOD OF MAKING A TUBULAR MEMBER BACKGROUND OF THE INVENTION Field of the Invention This invention relates to apparatus for rolling a flat strip of material laterally into a tubular-member having a spiral cross section with a minimum overlap of 360, and can be applied to the manufacture of insulated conductors.

Description of the Prior Art Flexible materials such as paper tend to follow their own natural line when being fonned and this line tends to vary according to the tension applied to the strip of material. For this reason'a solid forming tool comprising one or more holes in metal blocks, each having a profile designed to position the flexible strip during the forming operation, will distort the strip from its natural line in all but one specific set of operating conditions. This presupposes that it is possible to produce an ideal profile for one set of conditions. Where a considerable overlap is required'at the seam of the formed tube, distortion from the natural line of the flexible strip can set up high fric- A tional resistance due to the pressure produced between the overlapping surfaces. This in turn produces more distortion which, with some materials produces a cumulative effect which results in the failure of the flexible strip.

A forming tool is thus required which allows the strip to follow its natural line over most of its path through the tool yet constrains the strip at intervals along the path in such a way that the desired forming operation takes place.

SUMMARY OF THE INVENTION According to the present invention there is provided apparatus for rolling a flat strip of material laterally into a tubular member having a spiral cross section. The material includes an inner layer and an outer layer which overlaps the inner layer by at least 360. A plurality of narrow elements positioned at intervals along an axis, each having an aperture through which the axis passes, the apertures in a first group of adjacent elements being profiled so that they define a first tapering passageway with a slot in communication with the passageway along one side thereof, and the apertures in a second group of elements being profiled so that they define a second tapering passageway whose larger end envelopes the smaller end of the first passageway, the arrangement being such that when the strip of material is drawn through the elements along the axis the first group forms the inner layer of the tubular member leaving at least half the width of the strip outside the first passageway and projecting into the slot, and the second group wraps the remaining unformed width of the strip around the inner layer to form the outer layer, tension being maintained in the strip as it passes into the apparatus so that the portion of the strip projecting into the slot is prevented from entering the first passageway.

An embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a side cross-sectional view of apparatus according to the invention;

FIG. 2 shows a plan view of each of the individual plates in the apparatus of FIG. 1;

FIGS. 3 and 4 are cross-sectional views of tubular members made by the apparatus of FIGS. 1 and 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, the apparatus includes a base 1 to which are rigidly fixed a plurality of thin plates 2 to 8. The plates are positioned perpendicular to an axis 9 and each plate has an aperture 10 therein through which the axis passes. The apertures may be open, as in plates 2 to 5, or closed as in plates 6 to 8.

The plates 2 to 5 form a group whose apertures define a cone II and a slot 11a in communication with one side of the cone. The plates 6 to 8 form a second group the apertures of which define a cone 12 whose larger end envelopes the smaller end of the cone 11,.

In operation, a strip of material to be formed into a tube is drawn in the direction of the arrow along the axis 9. The plates 2 to 5 form the inner layer of the complete tubular member, back tension being applied to the strip so that at least half the width of the strip projects into the slot and is prevented from entering the cone ll. Thereafter the plates 6 to 8 wrap the projecting width of the strip around the inner layer to form the outer layer. In FIG. 2 cross sections 13 of the strip are shown schematically as it passes through the plates 2 to 6, and an enlarged cross section of the strip as it emerges from the plate 8 is shown in FIG. 3.

In the apparatus of this invention small variations in the pressure between the overlapping surfaces of the flexible strip will cause minor variations in the path of the outer'surface of the strip between the plates, thus avoiding a build up of frictional resistance.

To this end we have found it preferable to position the plates so that the point at which contact is first made between the overlapping surface lies between plates; in the-embodiment above between the plates 5 and 6.

The shape of the plates correspond to the cross sections of the equivalent solid die, but in some plates further superfluous material has been removed from where it would contact the strip to leave the minimum necessary to carry out the forming operation. This further reduces the friction between the apparatus and the strip. Plate 5 is such a plate where the maximum amount of material has been removed from contact with the strip. A suitable material for the plates is tungsten carbide.

It is to be understood that for any given strip material, strip size, and application, the number and positioning of the plates will have to be chosen accordingly. Also the material beyond theedges of the apertures, which serves only to give rigidity to the structure, may in some cases be dispensed with. Thus for some applications portions of thick wire bent into the shapes of the various apertures and fixed to the base may suffice.

Also, the apertures 10 have been shown as defining regular cones 11 and 12. In some cases, to reduce friction still further, the apertures may be designed to define tapering passageways other than regular cones.

The apparatus may be used, for example, to insulate a wire conductor with a paper strip. One edge of the strip is coated on one face with adhesive, e.g., a starch based paste, prior to the passage of the strip through the apparatus. The strip is drawn through the apparatus with the coated edge 14a outside the cone 11, and on the opposite side of the strip to that against the respective edges 14 of the plates 2 to 4. The wire conductor is drawn through the apparatus at the same time as the strip with the strip located between the wire and the edges of the apertures. Forward tension to draw the insulated conductor through the apparatus may be applied in the manner described in our copending application Ser. No. 589,108 filed Oct. 24, 1966 and assigned to the same assignee as the instant application. The insulated conductor is wound round a capstan with the outer edge of the paper strip between the capstan and the conductor. Radial pressure is applied to the overlapping edge for such time as is necessary for the paste to set.

In order that the wire conductor is located in the center of the insulation, the portion of the width of the paper strip which forms the inner layer of the insulation may be longitudinally corrugated prior to drawing the strip through the apparatus. A cross section of such an insulated conductor 15, is shown in FIG. 4. The corrugations are produced by passing the paper between six pairs of rollers, each successive pair having one more corrugation form. When formed around the wire and enclosed in an outer layer, the corrugations form a relatively rigid support for the wire.

It is to be understood that the foregoing description of specific examples of this invention is not to be considered as a limitation of its scope.

What is claimed is:

l. A method of making a tubular member from a flat member comprising positioning a plurality of apertured guides at intervals along an axis to define successive first and second rounded tapering passageways with the larger end of the second passageway enveloping the smaller end of the first passageway, the first passageway having a slot formed along one side, drawing a flat strip of material along the axis through said passageways with a portion of the width of the strip within the first passageway and a portion projecting into the slot and maintaining tension in the strip as it passes into the apertures so that the portion of the strip within the first passageway is spirally wound to form an inner layer and the portion of the strip projecting into the slot is prevented from entering the first passageway and thereafter enters the second passageway to be spirally wrapped around the inner layer to fonn an overlapping outer layer.

2. The method claimed in claim 1 wherein the strip is of insulating material and an electrical conductor is drawn through the apparatus at the same time as the strip so that the tubular member is formed round the conductor.

3. The method claimed in claim 2 wherein before the strip is drawn through the apparatus an adhesive coating is applied along one side of the strip adjacent that edge which is to project into the slot, said side being that which becomes the underside of the outer layer.

4. The method claimed in claim 3 wherein the portion of the strip which is to form the inner layer is longitudinally corrugated before being drawn through the apparatus in order to locate the conductor at the center of the insulation.

5. The method claimed in claim 1 wherein at least half the width of the strip projects into said slot and the outer layer overlaps the inner layer by at least 360.

6. The method claimed in claim I wherein the guides are positioned along the axis so that the point at which the overlapping layers come into contact is between guides. 

2. The method claimed in claim 1 wherein the strip is of insulating material and an electrical conductor is drawn through the apparatus at the same time as the strip so that the tubular member is formed round the conductor.
 3. The method claimed in claim 2 wherein before the strip is drawn through the apparatus an adhesive coating is applied along one side of the strip adjacent that edge which is to project into the slot, said side being that which becomes the underside of the outer layer.
 4. The method claimed in claim 3 wherein the portion of the strip which is to form the inner layer is longitudinally corrugated before being drawn through the apparatus in order to locate the conductor at the center of the insulation.
 5. The method claimed in claim 1 wherein at least half the width of the strip projects into said slot and the outer layer overlaps the inner layer by at least 360*.
 6. The method claimed in claim 1 wherein the guides are positioned along the axis so that the point at which the overlapping layers come into contact is between guides. 